Electroluminescent (EL) lamps are well-known. An EL lamp can be thought of as a thin capacitor having a dielectric sandwiched between the electrodes of the capacitor, with at least one electrode being transparent. When an alternating electric field is applied to the capacitor, particles having electroluminescent properties (e.g.; phosphor) suspended in the dielectric, emit light.
One aspect of EL lamp display technology which has previously posed a number of problems is in the design of multi-lamp EL displays. This type of display has a number of EL lamps printed on a single sheet. In such situations, the requirements of adhesion, providing conductive paths, supplying the power supply waveform to various parts of the display as well as providing the required degree of physical resilience, may be difficult to meet.
Known methods of fabricating single and multi-lamp displays have not been ideal in that, when laying conductive paths (or `traces`) on an insulating UV dielectric material, adequate adhesion to the adjacent substrate has been difficult to achieve. Further, the electrode shape (and therefore illuminated EL lamp shape) may need to have overlaid thereon conductive traces, the number of which depending on the 2-dimensional topology of the EL display. The shapes of the desired EL lamp is governed by the two dimensional shape (or `image`) of the electrodes at the back of the EL display and the phosphor. These electrodes are usually in the form of a silver conductive layer applied to a phosphor and dielectric layer combination. A known method of passing conduction traces over conductive areas of the EL display is to lay tracks of UV dielectric along the desired conduction path (usually between the power supply terminals and the rear electrode), lay down a silver conductive trace and then apply a layer of UV dielectric over the top of the trace. This insulates the trace from both the rear electrode and the front electrode areas which are exposed between lamp elements. The specifics of this technique will be discussed in more detail below.
Problems have previously been encountered at the point where traces 17 pass over the edge of a particular electrode ("B" in FIG. 2). At this point, the edge of the electrode can be thought of as a step when viewed in cross-section. At this point, the UV dielectric layers (30, 16a, 16b) and the trace 17 must traverse a relatively sharp discontinuity at the edge of the electrode (14a, 14b). This can lead to thin spots in the silver trace at the step. Such thin spots are known to be prone to burnout resulting in lamp failure. A further problem is that the UV dielectric is known to be prone to cracking at the points where the trace terminates.
In multi-lamp displays, it is usually necessary to lay a relatively large number of traces across various sections of the EL display. Such traces must be effectively insulated from any electrode material (front or rear) or other trace sections over which they pass. Where possible traces are routed around various parts of the lamp display. However, for complex display topologies, it is often necessary to lay these traces directly over the top of any electrode areas while avoiding the creation of any unwanted conduction paths between the electrode and the power supply conduction trace.
Accordingly, it is an object of the invention to provide an improved EL lamp having enhanced resilience, reduced susceptibility to thin spots and hence burnout as well as increased longevity coupled with an ability to be driven at increased lamp brightness levels. A further object of the present invention is to provide the public with a useful choice.